The objective of this project is to generate preliminary data testing the vibrissal motor system (VMS) of rodents as a model for experimental studies of the facial muscles in the orofacial region. This will be accomplished by employing three representative species (golden hamster, rat, guinea pig) to test the general hypothesis that different types of orofacial behavior (e.g., different categories of vibrissal movement) reflect different patterns of organization of the facial muscles. Two specific aims are designed to test two specific hypotheses regarding likely levels of organization. Hypothesis (1) is that homologous facial muscles with different specific actions have different physiological properties. To test this, Specific Aim (1) is to examine the histochemical fiver type composition of the vibrissal facial muscles in each species, and to compare the three species. Hypothesis (2) is that homologous facial muscles with dissimilar functions have dissimilar patterns of neural organization. To test this, Specific Aim (2) is to map (via horseradish peroxidase labeling) the distributions of the motoneuron cell bodies of the vibrissal facial muscles in the brainstem facial motor nucleus of each species, and to compare the three species. A VMS model of the facial musculature would provide new information on the functional properties of facial muscles. This could be valuable clinically in muscle transposition for orofacial paralysis by enabling better functional matching of the transposed muscle and pretraumatized, normal facial muscles.